Method of forming a conductive metal region on a substrate

ABSTRACT

There is disclosed a method of forming a conductive metal region on a substrate, comprising depositing on the substrate a solution of a metal ion, and depositing on the substrate a solution of a reducing agent, such that the metal ion and the reducing agent react together in a reaction solution to form a conductive metal region on the substrate.

The present invention relates to the field of forming conductive metalregions on substrates.

BACKGROUND TO THE INVENTION

There are many industrial applications for conductive metal regions onsubstrates, particularly processes which enable the conductive metalregions to be formed according to a pattern. An important application isthe manufacture of printed circuit boards, upon which metal layers areformed into a pattern to electrically connect different components andelectrical devices according to a predetermined arrangement. Otherapplications include aerials and antennae, such as those found in mobiletelephones, radio frequency identification devices (RFIDs), smart cards,contacts for batteries and power supplies, arrays of contacts for flatscreen technologies (liquid crystal displays, light emitting polymerdisplays and the like), electrodes for biological and electrochemicalsensors, smart textiles, and decorative features.

In most of these applications, the metal region must be conductive and ahigh level of conductivity is desirable, or in some cases essential.

One known method for preparing a conductive metal region on a substrateincludes the step of inkjet printing a liquid including metallicnanoparticles. The printed liquid is then heated to fuse chemicalcomponents of the liquid and evaporate the solvent. The nanoparticlesare thus brought into contact with each other and so conduct. However,these materials do not have a conductivity approaching that of bulkmetal. The heating step is not only inconvenient, but prevents thetechnique from being used with low melting point plastic substrates.

One example of this technique is described in “Metallisations byDirect-Write Inkjet Printing”, presented at NCPV Program Review Meeting,Lakewood, Colo. 14-17 Oct. 2001, by C. Curtis et al. Digital inkjetprinting techniques are used to print a pattern of metal organicdecomposition inks, with and without nanoparticle additions. Fordepositing silver, an organometallic compound such assilver(hexafluoroacetylacetonate)(1,5-cyclooctadiene) is dissolved in anorganic solvent to which silver particles are added which aresufficiently small to avoid clogging the 10-50 micron inkjet printinghead orifice. The ink is then applied by a digitally controlled inkjetprinter, which deposits an ink pattern across the substrate. The ink isthen heated to form a pattern of nanoparticles, which provide the bulkof the conductivity, electrically joined to some extent by residualsilver compounds. The technique provides good conductivity silverregions. However, the process is complicated for the preparation ofcopper regions by a need to operate in an inert atmosphere and theresulting copper films have resistivities which are several orders ofmagnitude worse than bulk copper metal. Although this technique providesa convenient means of preparing patterned metal layers on substrates, itrequires an inconvenient annealing step and does not provide layers withconductivity close to that of bulk metal.

One technique which is known to provide metal layers with conductivityclose to that of bulk metal is the electroless plating process. Theelectroless plating process is a solution chemistry plating techniquewhich has been used for many years to apply a conductive metal coatinglayer to a substrate, which may be flat or shaped. A substrate isimmersed in a succession of baths. The resulting conductive metal layermay be used as formed, or may undergo a subsequent electrodepositionprocess to increase the thickness of the conductive layer. Acommercially important technique is the so-called “plate through hole”process which has been used for over 30 years to metallize drilled holesin printed circuit boards by electroless techniques, for subsequentelectroplating.

A generic example of the electroless process is as follows. Firstly, aplastic substrate is etched in a chromic acid/concentrated sulphuricacid bath at 68±2° C. to microscopically etch the surface of theplastics substrate, ensuring good adhesion of the copper to the plasticssubstrate. Secondly, any hexavalent chromic species left on the plasticssubstrate are neutralised in a bath comprising approx. 30% concentratedhydrochloric acid at around 50° C. The plastics substrate is then addedto a third bath in which an activator is added to prepare the plasticssubstrate surface to absorb the catalyst in the next step. This thirdbath is typically approx. 30% concentrated hydrochloric acid, at roomtemperature.

Next, the plastic substrate is dipped into a fourth bath which includesa dilute solution of a palladium colloid along with tin salts. Thecolloid deposits on the surface of the plastic to catalyse thedeposition of copper in the subsequent plating step. This bath includesa high proportion of tin salts, approx. 30% concentrated hydrochloricacid, and operated at room temperature. The fifth bath into which theplastics substrate is dipped includes an accelerator which activates theadsorbed palladium, improving the speed and uniformity of deposition.Accelerator baths include around 30% concentrated hydrochloric acid.

Finally, the activated plastics substrate is dipped into a sixth bathincluding a plating solution which, catalysed by the palladium colloidon the plastic substrate, causes copper to deposit onto areas of theplastics substrate which were coated with the catalyst. The platingsolution include a copper salt, formaldehyde as a reducing agent, andsodium hydroxide to activate the formaldehyde. The composition of theplating solution must be carefully temperature controlled, with atemperature of 45±2° C. being appropriate for some commerciallyapplicable compositions. At a lower temperature, plating does not takeplace. At a higher temperature, plating takes places spontaneously andthe copper in the bath plates out. The copper salt, formaldehyde andsodium hydroxide must be stored separately as the combined solution isunstable.

The electroless copper deposition is used extensively and has theimportant advantage of producing highly conductive metal layers. Theconductivity of the resulting metal layer is usually close to that ofthe corresponding bulk metal.

However, a key disadvantage is that as plating is a bath process, theentire surface of the substrate is usually metallised. The process doesnot in itself allow the deposition of a metal in a pattern, as isrequired for many of the applications discussed above.

The process has several other limitations. Firstly, the process isrelatively complex, often requiring at least 6 baths, and so is suitableonly for use at specialist manufacturing facilities. Slight errors incomposition or deviations from the optimum temperature can result in themajority of the copper in the plating solution spontaneouslyprecipitating, wasting chemicals. Furthermore, the metal ions in thewaste products can be toxic to the environment and so require expensivewaste processing procedures. The high price of Palladium (and thevolatility in the price of Palladium) lead to further high costs andeconomic uncertainty in catalysed procedures.

Several approaches to preparing a patterned metal layer by way of theelectroless process have been described. Perhaps the simplest techniqueis to form the metal layer and then to apply a mask to parts of themetal layer which are to be retained, using an etchant to remove theremainder of the metal layer. This is wasteful of metal, laborious, oflimited reproducibility and produces components of variable quality.

An alternative approach to providing metal parts according to a patternis to press several component parts out of metal and then mount theseinto a device using additional substrate parts to hold the metalliccomponents. The technology known as insert moulding has developed thisconcept, aiming to reduce the number of separate components andmanufacturing costs. In insert moulding, a metal component is heldinside an injection moulding machine and the part is then moulded aroundthe metal component(s).

More recently, multi- and single-shot moulding technologies includingplating have been developed. A first component is injection moulded inplastic and then plated with a metal by the electroless processdescribed above. The plated part is then placed into a second mould andthe remainder of the part is formed around the plated part.

A still further development is injection moulding incorporating twodifferent grades of plastic, one of which is susceptible to plating inthe electroless plating procedure, and one of which is not. Such partsare created in a single moulding process and then plated, with only thefirst grade of plastic being plated. Although effective, this processcan be expensive and is therefore not suitable for use with low costitems.

U.S. Pat. No. 4,242,369 to Whittaker Corporation discloses compositionsand processes for jet printing of a metal or alloy. Minute uniformdroplets of a jet printing ink include at least one soluble salt of atleast one plate metal. The process is limited to depositing metal on abase metal surface which is less noble than the plate metal.

U.S. Pat. No. 4,668,533 to E. I. Du Pont de Nemours and Companydiscloses inkjet printing on a substrate using an ink comprising eitherfinely divided copper particles, or a metal containing activator, suchas a palladium (II) salt. The resulting printed substrate is then placedin a metal depositing bath which deposits a metal layer by theelectroless process described above. The pattern formed by the resultingmetal layer is determined by the pattern of droplets applied during theinkjet printing stage.

U.S. Pat. No. 5,751,325 to AGFA-Gevaert, N. V. discloses an inkjetprinting process which brings into working relationship, on a receivingmaterial, a reducible metal compound, a reducing agent for said metalcompound and physical development nuclei that catalyse the reduction ofsaid metal compound to metal. The process is used to produce highoptical density inkjet printed images rather than a conductive metallayer. The physical development nuclei are dispersed in an imagereceiving layer, such as a gelatin layer, overlying a substrate. Thus,metal is formed as discrete particles, around each physical developmentnuclei, within the gelatin layer. Discrete particles will not form anelectrically conductive region.

It is known to print conductive carbon (e.g. graphite) ink, or aconductive polymer, such as PEDOT, on a substrate and to thenelectrolytically plate the substrate. However, this is a complicatedmultistage process.

It is also known to generate a conductive polymer on a substrate byprinting a polymer, oxidising the polymer with permanganate and thenreacting the oxidised polymer with pyyrole to produce conductivepolypyrrole. This resulting material has low conductivity compared withconductive metals and so a subsequent electrolytic plating step may beapplied. Again, this is a complex multistage process.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, there is provideda method of forming a conductive metal region on a substrate, comprisingdepositing on the substrate a solution of a metal ion, and depositing onthe substrate a solution of a reducing agent, such that the metal ionand the reducing agent react together in a reaction solution to form aconductive metal region on the substrate.

It is not known precisely where the reaction between the metal ion andthe reducing agent takes place; however, the reaction preferably takesplace on or near or within the surface of the substrate, i.e. in situ,and not before the metal ion and reducing agent are in contact with thesurface of the substrate.

Preferably, the metal which is deposited is the only or uppermost metallayer in a product. Thus, the invention can be used to deposit all, orthe bulk of, the metal which is to form the conductive metal region in afinished product.

Unlike the method disclosed in U.S. Pat. No. 5,751,325, there is norequirement for physical development nuclei. The metal ion and thereducing agent react together in the reaction solution and form aconductive metal region on the substrate, instead of forming discretefine metal particles away from the substrate.

The reaction solution must have a composition such that the formation ofa conductive metal region on the substrate is thermodynamicallyfavourable. A conductive metal region will build up on the substrate andcatalyse further growth of the conductive metal region.

Whether this is thermodynamically favourable will depend on factorsincluding the temperature and pH of the reaction solution, the strengthof the reducing agent, the ease with which the metal ion can be reduced,the influence of complexing agents which can slow down the reduction ofthe metal ion, the properties of additional components of the reactionsolution and other factors well understood by persons skilled in thefield.

However, the composition of the reaction solution should not be suchthat spontaneous formation of metal particles takes place throughout thereaction solution. If this occurs, then instead of building up aconductive metal region on the substrate, fine particles will form whichare not physically connected to the surface of the substrate orelectrically connected to one another.

Deposition of solution on the substrate allows the amount of metal ionand reducing agent to be commensurate with the desired thickness of theconductive metal region. Deposition contrasts with immersion techniquessuch as the conventional electroless process where the substrate isimmersed in a bath including metal ion and reducing agent. Depositionrequires lower quantities of metal ion and reducing agent than animmersion process and can reduce waste. Furthermore, deposition reducesor obviates the difficulties in regulating the composition andtemperature of immersion baths.

The composition of the reaction solution may be selected so that it issufficiently unstable that the reaction between metal ion and thereducing agent in solution to form the conductive metal region on thesubstrate takes place spontaneously. However, the reaction solutionshould not be composed so that it is so unstable that a fine powder ofconductive metal forms spontaneously throughout the reaction solution,instead of forming a conductive metal region on the substrate.

One skilled in the art can readily adjust the composition of thereaction solution to prepare a reaction solution which willspontaneously plate out on the substrate, but not throughout thereaction solution.

The reaction between the metal ion and the reducing agent in solution toform the conductive metal region on the substrate may be activated by anactivator. In this case, the reaction between the metal ion and thereducing agent to form the conductive metal region on the substrate neednot take place spontaneously were it not for the presence of theactivator.

The activator may already have been applied to the substrate. Theactivator may be a component of the substrate. The activator may beapplied to, preferably deposited on, the substrate as an initial stage.

Preferably the activator is a catalyst which catalyses the reactionbetween the metal ion and the reducing agent. Appropriate catalystslower the activation energy and allow the metal region to formspontaneously on the substrate.

Preferred activators include fine metal particles or a metal layer(which functions as catalyst). The activator may comprise a component ofa reaction which forms fine metal particles or a metal layer in situ,for example metal ions or reducing agent which can react in a reactionsolution of metal ions and reducing agent to form fine metal particlesor a metal layer which functions as a catalyst for the subsequentmetallisation reaction. In this case the metal which comprises theactivator is typically different to the metal which forms the bulk ofthe conductive metal layer in the finished product. For example, anorganic acid salt of a transition metal, such as palladium acetate maybe deposited (preferably inkjet printed), preferably with one or morebinders, then reduced to palladium in situ by application of reducingagent (preferably by inkjet printing, but potentially by anymetallisation process including immersion in a bath of reducing agent).A solution of a different metal ion, e.g. copper, nickel or silver ions,is then deposited thereon, as is a solution of a reducing agent, by themethod of the present invention. Preferably, the resulting reactionsolution is autocatalytic, i.e. once its component metal startsdepositing, further metal will deposit thereon. The catalyst metalfunctions to catalyse the formation of metal from the autocatalyticsolution thereon, to start the deposition process.

Suitable activators include organic acid salts of transition metals, forexample, palladium acetate or palladium proponate. Palladium acetate hasbeen found to have good solvent solubility, is readily printable byinkjet techniques, and dries quickly to give high print quality and goodedge definition. Many other palladium salts, such as palladium chloride,are also suitable. Alkanoate salts are preferred. Alternative activatorsinclude salts, complexes or colloids of transition metals, or particlesof bronze, aluminium, gold or copper.

A suitable solvent for the deposition of an organic acid salt of atransition metal is a 50/50 mixture of diacetone alcohol andmethoxypropanol. Preferably, the organic acid salt of a transition metalconstitutes 1-3% by weight of palladium acetate, most preferably 2% byweight of the deposited liquid. An equivalent concentration of anotherorganic acid salt of a transition metal can be employed.

An alternative solvent is a 50/50 mixture of toluene andmethoxypropanol. Approximately a 2 % by weight solution of palladiumacetate in this solvent is preferably. Preferably a co-solvent is addedto increase viscosity for inkjet printing.

The activator/catalyst may be a second metal different from the firstmetal. The second metal may be formed by depositing ions of the secondmetal and a reducing agent on the substrate, such that the second metalions and the reducing agent react together in a reaction solution toform a conductive metal region on the surface. In this case, the firstmetal will preferably form the bulk of the conductive metal which isdeposited.

A catalytic metal region, or fine metal powder may be formed by firstdepositing (preferably by inkjet printing) of one or more of metal ion,reducing agent or base, preferably with a binder or in a chemicalformulation which forms a solid layer, and then depositing whichever ofmetal ion, reducing agent and base has not already been depositedthereon. This forms a conductive metal region or an area of fine metalparticles.

In one embodiment a metal ion (e.g. palladium) is applied to thesubstrate by inkjet printing (and preferably dried/cured/hardened insitu) and then the substrate is either immersed into a bath of reducingagent or has reducing agent deposited thereon (e.g. by inkjet printing)forming a conductive metal region or area of fine metal particles on thesubstrate to function as catalyst. This is then suitable formetallisation by deposition on the substrate of a solution of a metalion, and deposition on the substrate of a solution of a reducing agentas before. Typically, the metal ion deposited to form the bulk of theresulting conductive metal region is different to the metal iondeposited to form the catalyst. In alternative embodiments, reducingagent is applied first to the substrate, which is then immersed in asolution of metal ion and base or has metal ion deposited thereon byinkjet printing.

Whether or not an activator is required, the solution of metal ion andthe solution of reducing agent may be deposited in a plurality ofseparate component solutions, or in a single component solution.

A pH altering reagent, typically an acid or base may also be deposited,to activate the reducing agent. The acid/base may be deposited in acomponent solution with either or both of the metal ion and the reducingagent. The base may deposited in a separate component solution to eitheror both of the metal ion and the reducing agent. The acid/base may alsobe deposited with the activator. Thus, the metal ion may be stored in acomponent solution at a pH at which it will not spontaneously formmetal.

For example, the metal ion, the reducing agent and an acid/base may bedeposited in three separate component solutions which mix together onthe substrate and form the reaction solution.

In another example, the metal ion and the reducing agent are depositedin a first component solution, and an acid/base is deposited in a secondcomponent solutions, such that the first and second component solutionsmix together on the substrate and form the reaction solution.

In a further example, a single component solution includes the metalion, the reducing agent and the acid/base.

It is generally preferred to have as few component solutions as possibleto minimise the complexity of the deposition process. However, where thereaction solution is not sufficiently stable to be used reliably withthe chosen deposition process, the separation of components of thereaction solution into a plurality of component solutions allows thereaction solution to be prepared from more stable component solutions.

Where an activator is used, the method preferably includes the step ofdepositing the activator on the substrate before deposition of acomponent solution. More preferably, the activator is deposited beforeeither or both of the metal ion or the reducing agent are deposited onthe substrate. The activator is therefore located on the substrate andso favours formation of a conductive metal region on the substraterather than formation of fine particles of conductive metal throughoutthe reaction solution.

The activator is preferably deposited in an activator solution.Preferably, the solvent for the activator solution is primarily orentirely non-aqueous. The solvent is preferably allowed to substantiallyevaporate or otherwise dissipate prior to deposition of one or morecomponent solutions thereby forming a layer. This reduces or preventsdiffusion of the activator away from the substrate where it might leadto excessive formation of conductive metal regions which are not on thesubstrate. Typically, between a few seconds and a few minutes may berequired to allow volatile components to dissipate, with a time ofaround 30 seconds being typical, before one or more component solutionsare deposited thereon.

Optionally, the substrate is pretreated before an activator liquid isdeposited thereon. This causes the activator liquid to dry rapidly andspread less, achieving thinner lines. For example, a Melinex substrate(Melinex is a Trade Mark) was heated at 350° C. for 4 seconds using aheat gun.

Preferably, the activator is deposited in a solution including achemical component which promotes adhesion of the activator to thesubstrate, for example, a polymer. Suitable adhesion promoters retainthe activator on the surface of the substrate so that the activator isnot washed into the reaction solution when a further component solutionis deposited. Suitable polymer adhesion promoters includepolyvinylpyrollidinone and polyvinylbutyral.

Where, as is preferred, the activator is deposited in a primarily orentirely non-aqueous solution, the activator may be deposited in asolvent selected dependent on the nature of the substrate. Preferably,the solvent is selected to partially dissolve the substrate to enablethe activator to penetrate the substrate and improve adhesion of theresulting conductive metal region to the substrate. Thus, the activatoris preferably deposited in solution prior to the deposition of either orboth the metal ion and the reducing agent. However, the solvent must notbe too aggressive or not only will the substrate be damaged, but thesubstrate will swell and the activator will penetrate too far into thesubstrate, so that it is no longer present at the surface of thesubstrate in sufficiently quantity to reliably activate the depositionof the conductive metal ions.

The substrate may be pretreated prior to the deposition of activator toimprove adhesion. For example, the substrate may be immersed in a waterbased oxidising solution, as it known in the conventional electrolessprocedure. The method may also include the deposition of a preparationreagent on the substrate, such as a solvent which etches the substrateor a water based oxidising solution, prior to deposition of thecatalyst.

The activator solution may comprise one or more of the metal ion, thereducing agent or a base/acid.

The component solution which comprises the metal ion may furthercomprise a complexing agent. A complexing agent such as EDTA binds metalions, slowing or preventing the rate of reduction of the metal ion bythe reducing agent. A complexing agent can therefore prevent spontaneousformation of metal in the component solution comprising the metal ion.

A single component solution may be deposited, or a plurality ofcomponent solutions may be deposited which are mixed together during oras a result of deposition. If metal ion and reducing agent are depositedat separate times, they may be deposited in either order. Where aplurality of component solutions are deposited, they may be depositedsequentially or simultaneously. It is preferred that a plurality ofcomponent solutions are deposited sequentially and a single solution, orcombination of solutions is allowed to partially or fully dry-out, cureor otherwise harden before one or more further component solutions aredeposited thereon. We have found that this procedure can allow betteradhesion of the conductive metal region to the substrate and can improvethe quality of patterning.

Where a solution (perhaps formed from a plurality of solutions)(hereafter ‘first liquid’) comprising an activator for the conductivemetal region forming reaction, is allowed to partially or fully dry-out,cure or otherwise harden on the substrate to form a first solid layer,before one or more further component solutions (hereafter ‘secondliquid’) is deposited thereon to begin the conductive metal regionforming reaction, and where the first liquid comprises an activator fora second solid-layer-forming chemical reaction, the first liquid isselected so that the first solid layer adheres to the substrate and ispermeable to the second liquid which comprises one or more reagents forthe second solid layer-forming chemical reaction.

Thus, the activator is adhered to the substrate by virtue of itsinclusion in the first solid layer (whether by entrapment,immobilisation or other means).

When the second liquid is brought into contact with the first solidlayer, the second liquid penetrates the first solid layer, allowing thesecond liquid to access the activator within the first solid layer. Thesecond solid-layer-forming reaction can thus take place, on or in closeproximity to or within the substrate substance, producing the desired(second) solid layer (of conductive metal) on the substrate.Furthermore, penetration of the second liquid into the first solid layermay result in the (second) solid layer of material intermingling withthe first solid layer, thereby enhancing adhesion of the (second) solidlayer (of conductive metal) to the substrate via the adhered first solidlayer.

As the activator is located in a layer on the surface of the substrate,metallisation will occur on the first layer in preference to theformation of fine particles of metal in the second liquid.

The first liquid need not necessarily be a solution. One or morecomponents thereof may be a solid, colloid etc.

Preferably, the first liquid comprises a first chemical functionalitywhich is insoluble in the second solvent.

Preferably also, the first liquid comprises a second chemicalfunctionality which is at least partially soluble in the second solvent.Such a second chemical functionality will at least partially dissolvesin the second solvent, allowing the second solvent to penetrate thefirst solid layer and contact the activator. The first chemicalfunctionality retains sufficient integrity to adhere to the substrateand the second solid layer.

The method may include the further step of chemically converting the oneor more reagents to an active or catalytic form. For example, palladiumacetate may be reduced in situ by a subsequently applied reducing agentsolution, forming palladium metal which can catalyse deposition of metalthereon when the second liquid is applied.

The first liquid may comprise a second chemical functionality which canswell in the second solvent or take up the second solvent.

The first and second chemical functionalisation may be separatemolecules, or groups of molecules, or may be or become part of the samemolecules. Typically, they are two separate binders.

The first chemical functionality only needs to be sufficiently insolublein the second solvent to retain integrity while the second solid layeris formed. Also, the first solvent is preferably sufficiently aggressiveto the substrate to allow the first layer to allow the first liquid topenetrate therein, increasing adhesion of the first solid layer to thesubstrate, and thus also increasing the adhesion of the second solidlayer to the substrate (via the first solid layer).

The first and second solvents are preferably different. This allows thefirst solvent to be selected to be appropriate for the formation of thefirst layer and the adhesion of the first layer to the substrate, whilstthe second solvent can be selected to be appropriate for the formationof the second layer. Preferably, the second solvent is water. Preferablyalso, the first solvent is selected to partially dissolve or otherwisepermeate into the substrate, improving adhesion of the first layer tothe substrate. Thus, aqueous metallisation chemistry and a non-aqueousfirst solvent can be utilised in different steps of the same process.Preferably, the first solvent is partially or entirely non-aqueous.

Thus, the first liquid may comprise one or more second chemicalfunctionalities which are soluble in the second solvent, such aspolyvinyl pyrrollidinone, which is soluble in water. Alternativesinclude polyacrylic acid, polyvinyl acetate, polyethylene imine,polyethylene oxide, polyethylene glycol, gelatin or copolymers thereof.The soluble components may dissolve when the second liquid is broughtinto contact with the first solid layer. For example the polyvinylpyrrollidinone will dissolve in contact with an aqueous solution ofmetal ion and reducing agent usable to form a conductive metal region onthe first solid layer. Around 5% by weight of polyvinyl pyrrollidinonein the resulting solid layer is appropriate.

The second chemical functionality could instead (or as well) comprise awater swellable monomer and/or oligomer such as HEMA (2-hydroxyethylmethacrylate), GMA (glyceryl methacrylate) or NVP (n-vinylpyrrolidinone). Other monomers and/or oligomers which are themselvesswellable in the solvent of the second liquid and/or are swellable whenpolymerised could be used instead. This allows the second liquid topermeate into the first solid layer, improving adhesion and allowingaccess to more activator than just what is present on the surface of thefirst solid layer.

The second chemical functionality could instead (or as well) comprise ahigh boiling point solvent miscible with the solvent of the secondliquid. For example, NMP (n-methyl pyrrolidinone) could be used when thesecond liquid is aqueous. This keeps the resulting polymer matrix openin the first solid layer allowing penetration by the second liquid andimproving the adhesion of the second solid layer to the first solidlayer. Alternative solvents include ethylene glycol, diethylene glycolor glycerol.

The first liquid could instead (or as well) comprise micro-porousparticles to create a micro-porous film structure. Micro-porousparticles could be organic (e.g. PPVP poly (polyvinyl pyrrolidinone)) orinorganic (e.g. silica).

The first liquid may solidify as a result of evaporation of the firstsolvent.

The process may be repeated (optionally with different first and secondliquids) to build up a multi-layer structure.

Preferably, the first liquid is curable; that is to say, able to undergoa chemical change as a result of which the liquid hardens, preferablysolidifies

The curable first liquid may be selected to have improved wettingproperties on one or more substrates than the second liquid. This allowsmore accurate and precise patterning than if the curable first liquidwas applied from the same carrier (e.g. water) as the second liquid,with fine features and better edge definition. There will typically beless bleed and feathering of the curable first liquid than if activatorwere applied to the surface by a different technique using a carrierwith poorer wetting properties. Improved wetting properties allow moreaccurate and precise patterning as successive spots of liquid along aline can be deposited further apart (by a technique such as inkjetprinting) allowing a lower volume of liquid to be used, and thusnarrower lines and finer features to be prepared.

This use of the first curable liquid comprising an activator isparticularly important where it is desirable to use inkjet printing todigitally pattern a material on a substrate. Many curable liquids arewithin the correct viscosity range to be inkjet printed.

The curable first liquid preferably comprises one or more componentchemicals which can undergo a reaction causing the liquid to harden.

Preferably, the curable first liquid comprises monomers and/or oligomerswhich can polymerise and/or cross-link in use, thereby hardening andforming a solid layer. Preferably, the resulting polymer forms a matrixwhich includes the activator. A curable first liquid including at leastsome oligomers will often have lower toxicity than if it included onlymonomers.

The first solid layer may be rigid, elastic or plastic (where or not itis formed by curing). Preferably, it need not necessarily finishhardening before the second liquid is applied.

Preferably, the first liquid is curable in response to a stimulus, forexample, electromagnetic radiation of a particular wavelength band (e.g.ultra-violet, blue, microwaves, infra-red), electron beams, or heat.Thus, the curable first liquid may be curable responsive toelectromagnetic radiation of a specific wavelength range (e.g.ultraviolet radiation, blue light, infra-red radiation), heat curable,electron beam curable etc. The liquid could be curable responsive to thepresence of one or more chemical species such as moisture or air.Preferably, the component chemicals are selected to undergo a reactionresponsive to one of the above stimuli.

Typically, the curable first liquid comprises one or more monomersand/or oligomers which can form a polymer, and constitute the firstchemical functionality. For example, monomers and/or oligomers whichreact to form a polymer, and an initiator which starts a polymerisationreaction responsive to one of the above stimuli. e.g. AIBN(2,2′-azobisisobutyronitrile) can be included to initiate apolymerisation reaction responsive to heat. Typically, an initiatorgenerates free radicals responsive to a stimulus. It is also possible touse an initiator which generates cations responsive to a stimulus.

Preferably, the monomers and/or oligomers are those known from the fieldof UV curable, or other curable inks proposed for inkjet printing ofcurable inks.

Preferably, the delay between depositing and curing the curable liquidis as short as possible. This reduces over-wetting of the substrate,which causes less of definition to the image. Preferably the delaybetween deposition and curing is 20 seconds or less.

Preferably, the curable first liquid comprises some monomers and/oroligomers having a high number of cross-linkable functional groups, suchas four or more, or even six or more functional groups. For example,Actilane 505 (which is a reactive tetrafunctional polyester acrylateoligomer supplied by AKZO Nobel UV Resins, Manchester, UK) is suitable,as is DPHA (dipentaerythritol hexaacrylate) which is a hexafunctionalmonomer supplied by UCB, Dragenbos, Belgium. These monomers and/oroligomers with a high number of cross-linkable functional groups aremore highly cross-linked than polymers formed from monomers with fewercross-linkable functional groups and can provide a stronger, more robustfilm with better adhesion to the substrate. Too high a proportion ofhighly cross-linkable monomers and/or oligomers would however form abrittle surface.

As the activator is also included in the first liquid it will typicallybe trapped within the first layer in a matrix formed, for example, by apolymer. The activator could also be immobilised as part of the matrix,for example, by including the activator on a molecule with a reactivegroup which reacts with monomer or oligomer units. The activator may beinitially inactive, and become active only once the first liquid hasformed the first solid layer, or in response to a stimulus, or when incontact with a component of the second liquid.

Where the second solid-layer-forming chemical reaction is to be areaction between metal ions and a reducing agent, to form a conductivemetal region, the activator may be one or more of metal ions, reducingagent and (optionally) an acid or base. The second liquid will be suchthat a second-layer-forming reaction begins when the second liquid is incontact with the first layer. Where the activator comprises metal ions,typically as metal salts or metal complexes (and perhaps also bases),the second liquid may comprise reducing agent and (optionally) anacid/base. The second liquid may also contain additional ions of thesame or a different metal. Where the activator comprises a reducingagent (and perhaps also acid/base), the second liquid will preferablycomprise metal ions, typically as metal salts or metal complexes. Thesecond liquid may comprise further reducing agent. Where the activatorcomprises base, the second liquid typically includes metal ions andreducing agent, and optionally further acid/base.

Where the first liquid is curable, it preferably does not include avolatile carrier which, in use, is evaporated off before the secondliquid is brought into contact with the first layer. Thus, substantiallyall of the constituents of such a curable first liquid preferably remain(albeit perhaps in chemically changed form) in the first solid layer.

However, the first liquid may include a volatile carrier. Typically, inuse, some or all of the volatile carrier evaporates or is evaporated offbefore the second liquid is brought into contact with the first layer.For example, the first liquid may comprise water or (preferably) one ormore organic solvents which, in use, are evaporated off before thesecond liquid is brought into contact with the first layer. The methodmay include a pause to allow a volatile carrier to evaporate before oneor both of applying a stimulus (if applicable) and bringing the secondliquid into contact with the first layer.

Preferably, the first liquid is deposited onto the substrate by inkjetprinting. Preferably, the second liquid is deposited on the first layerby inkjet printing. Where the first liquid and/or resulting first layerare patterned, the second liquid may be deposited according to the samepattern.

A component solution may be mixed from stock solutions prior todeposition. Mixing may take place immediately prior to deposition. Forexample, a component solution which is unstable might be mixed fromstock solutions including constituents of the component solution priorto deposition. More particularly, a component solution including boththe metal ion and the reducing agent might be mixed from separate stocksolutions of the metal ion and the reducing agent immediately prior todeposition. This allows unstable solutions to be deposited onto thesubstrate.

It is generally preferred initially to deposit on the substrate acomponent of the reaction (in the form of a solution of a metal ion, asolution of a reducing agent or an activator) and for that component todry, cure or otherwise harden to form a solid layer on the substrate.Other component(s) of the reaction are subsequently deposited in liquidform (in one or more steps) on the solid layer.

A currently preferred method involves initial deposit of an activator,e.g. palladium acetate, which is dried, cured or otherwise hardened insitu to form a solid layer on the substrate surface. The palladiumacetate is optionally treated with DMAB (dimethylamineborane) to reducepalladium ions to palladium metal. A solution of a metal ion, e.g.copper sulphate, and a reducing agent, e.g. formaldehyde, (with base toadjust pH) are then deposited on the palladium metal layer, with thesefurther reagents conveniently mixed together in a single solution.

Preferably, the activator is deposited on the substrate in a pattern,thereby leading to the formation of one or more patterned conductivemetal regions. Component solutions may be deposited in the same pattern,over the activator, or more generally across the substrate.

A pattern may also be formed by depositing a component solution in apattern. This is particularly appropriate where activator has beendeposited in a non-pattern specific distribution across the substrate.

Preferably, deposition in a pattern is carried out by inkjet printing.Preferably, the activator solution is inkjet printed. Alternatively oras well, one or more component solutions may be inkjet printed. Otherdeposition techniques, such as spraying, may be employed.

Inkjet printing can be used to provide a quicker process, with fewersteps, than the conventional electroless procedure. Inkjet printingapparatus could potentially be cheaper than the capital equipmentrequired for the conventional electroless procedure and is more readilytransported than the immersion baths used in the conventionalelectroless procedure. Inkjet printing allows the deposition of verycarefully controlled volumes of liquid, allowing the correctstochiometry of metal ion and reducing agent to be deposited, reducingwaste. For example, where the metal ion is copper sulphate and thereducing agent is formaldehyde, the reaction products are sodiumsulphate and sodium formate which can readily be processed for disposal.Thus, substantially stochiometric amounts of metal ion and reducingagent may be deposited. Preferably, however, an excess of reducing agentto metal ion may be deposited, so that essentially all of the metal ionis consumed, reducing or avoiding metal-containing waste. The excessreducing agent may be washed away.

Another benefit of inkjet printing is that it is a digitally controlledprocedure, allowing different patterns to be applied using the sameapparatus. This is particularly important for one-off products,customised products, or a series of uniquely identifiable products.

Furthermore, as inkjet printing is a non-contact procedure, the presentmethod may be used with fragile substrates.

Inkjet printing may be achieved using continuous or drop-on-demandinkjet printing techniques, such as binary or raster continuous inkjet,and piezo or thermal drop on demand inkjet technologies. For example,U.S. Pat. No. 5,463,416 discloses a method of operating a drop-on-demandinkjet printer.

Where an acid or base is used, the inkjet print head preferablycomprises a ceramic material, such that liquid containing the acid orbase contacts only ceramic material in the inkjet print head.

Where there are a plurality of solutions to be inkjet printed, these maybe deposited by different nozzles or banks of nozzles in the same inkjethead, or by separate inkjet heads at the same time, or after a shortdelay.

The metal ion may be an ion of any conductive metal. Preferredconductive metals include copper, nickel, silver, gold, cobalt, aplatinum group metal, or an alloy of two or more of these materials. Theconductive metal may include non-metallic elements, for example, theconductive metal may be nickel phosphorus.

The metal ion is typically in the form of a salt. For example, coppersulphate. The metal ion might instead be present in a complex such aswith EDTA (ethylene diamine tetra acetic acid) or cyanide.

Examples of appropriate reducing agents are formaldehyde, glucose ormost other aldehydes, or sodium hypophosphite, glyoxylic acid,hydrazines or dimethylamineborane. A relatively mild reducing agents maybe used with readily reducible metal ions such as gold or silver, andstronger reducing agent may be required for less readily reducible metalions. The reducing agent should not be too strong however or metalparticles will spontaneously nucleate away from the surface of thesubstrate.

The substrate and/or the reaction solution may be heated to start and/orspeed up the process of deposition of conductive metal on the substrate.For example, infra-red light from an infra-red heater may be incident onthe reaction solution.

Suitable substrates include plastics material sheets and fabrics. Thesubstrate might be a material having thereon electrical components, suchas conductive, semiconductive, resistive, capacitive, inductive, oroptical materials such as liquid crystals, light emitting polymers orthe like. The method may include the step of depositing one or more ofsaid electrical components on a substrate, preferably by inkjetprinting, prior to forming a conductive metal region on the resultingsubstrate.

Similarly, the method may further include the step of depositing anelectrical component onto the resulting conductive metal region,building up complex devices. Said further deposition step may also becarried out using inkjet printing technology.

Thus, the method can be used as one stage in the fabrication ofelectrical items. It is particularly appropriate for use inmanufacturing electrical items which involve complex patterns, such asdisplays which include complex patterns of pixels. Other applicationsinclude the fabrication of aerials or antenna for car radio, mobilephones, and/or satellite navigation systems; radio frequency shieldingdevices; edge connectors, contact and bus connectors for circuit boards;radio frequency identification tags (RFID tags); conductive tracks forprinted circuit boards, including flexible printed circuit boards; smarttextiles, such as those including electrical circuits; decoration;vehicle windscreen heaters; components of batteries and/or fuel cells;ceramic components; transformers and inductive power supplies,particularly in miniaturised form; security devices; printed circuitboard components, such as capacitors and inductors; membrane keyboards,particularly their electrical contacts; disposable low cost electronicitems; electroluminescent disposable displays; biosensors, mechanicalsensors, chemical and electrochemical sensors.

Preferably, the conductive metal region forms a layer. Preferably,components of the reaction solution are selected so that the layeradheres to the surface of the substrate. The method may be repeated,depositing further metal ion and reducing agent in solution upon theconductive metal region so as to form a thicker conductive metal layer.Different metal ions may be used for a second or successive layers, thusbuilding up a material comprising layers of a plurality of differentmetals. Products including multiple layers of different metals may bebuilt up in this way, including products comprising layers alternativebetween two or more different metals. Alloys may be built up bydepositing a component solution comprising a mixture of metal ions, orby depositing a plurality of component solutions comprising differentmetal ions.

A preferred application of the method is as one or more steps in thefabrication of radio frequency identification tags (RFID tags). RFIDtags can send and/or receive identifying information to/from RFID tagdetectors. The method is applicable to both inductively and capacitivelycoupled tags, which may be active (i.e. including an internal powersource) or passive (not including an internal power source). Such tagstypically include a microprocessor (often including some memory), and aconductive antenna.

The invention extends to a method of manufacturing an RFID tag using oneor more of the procedures A, B or C below, and also to an RFID tagmanufactured using one or more of procedures A, B or C below.

In procedure A an antenna of a conductive metal is formed on a substrateby the method of the first aspect. Preferably, the antenna is aconcentric loop of conductive metal. This technique is applicable to themanufacture of active or passive RFID tags. The invention also extendsto a method of forming an aerial on a substrate (for any application) byforming a conductive metal region, configured to function as an aerial,on a substrate, by the method of the first aspect.

In procedure B a battery is formed on a substrate by forming two regionsof different conductive metals on a substrate by the method of the firstaspect, and electrolytically connecting the two regions by way of anelectrolyte (which may be inkjet printed), thereby forming anelectrochemical cell. A plurality of electrochemical cells may beelectrically connected in series or in parallel thereby increasing thevoltage and/or current available. The invention also extends to a methodof forming a battery by forming two regions of different conductivemetals on a substrate by the method of the first aspect, andelectrolytically connecting the two regions by way of an electrolyte(which may be inkjet printed). The invention also extends to a batteryformed by the said method.

In procedure C a microchip is applied to a substrate and then one ormore conductive metal regions are formed on the substrate by the methodof the first aspect of the present invention to make electricalconnections to one or more electrical contacts of the microchip. Theinvention also extends to a method of making an electronic device (notjust RFID tags) comprising the step of applying a microchip to asubstrate and then forming one or more conductive metal regions on thesubstrate by the method of the first aspect of the present invention.The invention further extends to an electronic device made by thismethod.

Preferably, this procedure includes the step (after the microchip hasbeen applied to the substrate) of measuring the location of themicrochip and then forming the conductive metal regions to makeelectrical connections dependent on the measured location of themicrochip. This has the benefit that the location where the microchip isapplied can vary within a tolerance that is higher than with knownmethods of locating a microchip, reducing costs.

The procedure may also include the step of forming a conductive metalregion on the substrate to function as a heat sink for a microchip,before applying the microchip thereon. Preferably also, the methodincludes the step of depositing a thermally conductive material(typically a thermally conductive adhesive) upon the heat sink (perhapsby inkjet printing) before the microchip is applied.

In procedures A, B and C above, a region of Conductive metal ispreferably formed on a substrate by inkjet printing.

The method of manufacturing an RFID tag may comprise the steps of inkjetprinting the substrate upon which the antenna, battery, heat sink and/orchip is deposited.

The method of manufacturing an RFID tag may comprise the step of inkjetprinting an over coat or protective layer of material (such as a polymerlayer) over the deposited components.

The method of manufacturing an RFID tag has advantages of simplicity andlow cost over known techniques.

The one or more component solutions should fulfil the specificrequirements of inkjet printing inks as regards viscosity, surfacetension, conductivity, pH, filtration, particle size and ageingstability. Humectants may be added to one or more component solutions toreduce evaporation. The particular values of these properties which arerequired are different for different inkjet technologies and suitablecomponent solutions fulfilling these properties can readily be devisedfor a specific application by one skilled in the art.

The method may include the further step of electrolytically platingadditional metal onto the conductive metal regions by known electrolyticplating techniques. The method may include the further step of platingadditional metal onto the conductive metal regions by the knownelectroless immersion procedure.

Alternatively, a sufficient amount of conductive metal may be formed onthe substrate that no further step of plating additional metal by knownelectrolytic or electroless immersion procedures is required.

According to a second aspect of the present invention there is providedan article comprising a substrate including a conducting metal regionprepared according to the method of the first embodiment.

Preferably, the conducting metal region is a layer.

According to a third aspect of the present invention there is provided amethod of activating the reaction between a metal ion and a reducingagent to form a conducting metal region comprising the use of an organicacid salt of a transition metal as an activator.

Many organic acid salts of transition metals have good solventsolubility, are readily printable by inkjet techniques, and dry quicklyto give high print quality and good edge definition. A preferred organicacid salt of a transition metal is palladium acetate which has the aboveproperties and also has the benefit of being commercially available inbulk at a reasonable price. Alternatives include palladium propanoate,butanoate etc. or other alkanoate salts of a transition metal,especially palladium.

In use, the organic acid salt of a transition metal is reduced to metalparticles or a metal layer which can catalyse deposition of metal(preferably a different metal) thereon, by the method of the firstaspect.

Preferably, the activator is deposited with a polymer to adhere thecatalyst to the substrate.

Preferably, the activator is added to a substrate and the conductingmetal region is formed as a layer on the substrate.

Preferably also, the activator is added to the substrate by inkjetprinting a solution including the activator.

DETAILED DESCRIPTION OF AN EXAMPLE EMBODIMENT

The following activator solution is prepared: Activator Solution % - byweight palladium acetate 2.0 diacetone alcohol 47.7 methoxy propanol47.7 polyvinylbutyral 1.6 potassium hydroxide 1.0

Palladium acetate is present as an activator. Diacetone alcohol andmethoxy propanol are mixed in this proportion to give a solvent whichevaporates sufficiently quickly to allow the palladium acetate to attachto the substrate before addition of the reaction solutions discussedbelow. However, the rate of evaporation is sufficiently slow that thisactivator solution can be conveniently inkjet printed. Polyvinylbutyralis present to help the catalyst adhere to the substrate.Polyvinylbutyral with a molecular weight of between 15,000 and 25,000 issuitable, such as grade BN18, available from Wacker. Potassium hydroxideis present to function as a base, activating the reducing agent below.

To make the above activator solution, a 30% solution of polyvinylbutyralis prepared in a 50/50 mixture by weight of diacetone alcohol andmethoxy propanol. A 3% palladium acetate solution is prepared in thesame solvent mixture using sonication over a period of 2-3 hours.Separately, a 10% solution of potassium hydroxide is prepared in thesame solvent mixture. These three solutions are then mixed and more ofthe same solvent mixture is added to make up the appropriate totalvolume to give the proportions specified above. The resulting fluid isbrown-orange translucent liquid which is then filtered through a 1micron GF-B glass fibre filter available from Whatman. A slight depositis sometimes visible on the filter paper.

The resulting activator solution has a viscosity of 3.91 cPs and asurface tension of 31.5 dynes/cm.

The following three component solutions are also prepared: Solution A% - by weight copper sulphate 1.63 sodium sulphate 3.21 EDTA, disodiumsalt 0.60 water 89.56 t-butanol 5.00

The copper sulphate is the source of the metal ion, here Cu²⁺. Sodiumsulphate is present to stabilise the copper sulphate. EDTA is acomplexing agent which forms a protective barrier around the copperions, without which a solution of this composition would immediatelyprecipitate out. t-butanol is a cosolvent which reduces surface tensionand improves wetting. Solution B % - by weight formaldehyde solution(37% by weight in water) 0.22 sodium formate 3.71 water 91.07 t-butanol5.00

Formaldehyde is present as the reducing agent. Solution C % - by weightsodium hydroxide 1.74 water 93.26 t-butanol 5.00

The function of sodium hydroxide is to activate the reducing agent whenthe solutions are combined.

Solutions A, B and C are shaken and then filtered through a 1 micronGF-B glass fibre filter, available from Whatman. Each solution had aviscosity of less than 3 cps.

Deposition

Firstly, the activator was deposited by inkjet printing. An XJ128-200print head, from Xaar, was primed with the activator solution and thenused to jet the activator solution onto the substrate. The resolutiondown web was adjusted to the particular substrate. For easily wettedsubstrates, 250 dots per inch (dpi) was used. For substrates which arewetted only with difficulty, 1000 dpi was used to ensure completewetting.

The XJ128-200 print head ejected droplets of 80 pL. The jettingfrequency was between 1 and 2 kHz and a throw distance of 1-2 mm wasused.

The activator was inkjet printed in a variety of patterns, such as solidblocks, thin lines, text, checked patterns and standard inkjet printingtest images.

After jetting of the activator solution, the printed activator solutionwas allowed to dry using an infra-red heater located just above thesubstrate. In some experiments, the printed catalyst solution wasallowed to dry under ambient conditions, without any additional heating.

Where the infra-red heater was used, 30 seconds was found to besufficient drying time.

Next, the 3 separate component solutions A, B and C were inkjet printedonto the dried activator. The three solutions were printed separately,in equal volumes, onto the same locations on the substrate, evenlyacross the whole printable surface area of the substrate, forming areaction solution in situ. The solutions were inkjet printed using a64ID3 print head, available from Ink Jet Technology. All parts of thisprint head which contact the fluid to be jetted are ceramic and so thishead is particularly suitable for printing very basic or acidic liquids.Jetting took place at 5 kHz. The waveform of the potential applied tothe piezoelectric printing head was selected to cause ejection ofdroplets of 137 pL.

The activator is reduced to form palladium particles on the surfacewhich catalyse formation of a copper metal region thereon. Once copperhas started depositing, the reaction is autocatalytic.

The reaction solution was allowed to remain in contact with thesubstrate until a suitable thickness of copper had been deposited.Typically, less than 5 minutes at room temperature were required toproduce a suitable layer of copper.

It was found that the copper regions could be formed quicker by heatingthe substrate with infra-red radiation. However, it was important toensure that the surface temperature did not rise above 50 degreescentigrade for many types of plastics substrates, to avoid warping thesubstrate.

Finally, any excess solution or dried salts were wiped or washed off thesubstrate, yielding a copper-plated sample where the copper platedregions correspond to the pattern in which the activator had been inkjetprinted.

Results

Copper was inkjet printed by this technique onto the followingsubstrates, and the strength of the adhesion between the depositedconductive metal regions and the substrate was qualitatively measured.Substrate Material Adhesion acrylic Good polystyrene Good polyethylenePoor through good, depending on grade delrin polyacetal homopolymer PoorHostaform or Ultraform polyacetal copolymer Poor ABS (Acrylonitrilebutadiene styrene) Good U-PVC Good silicone rubber Poor

(Delrin is a trademark of DuPont. Hostaform is a trademark of Hoechst.Ultraform is a trademark of BASF)

As a result we have demonstrated the printing of conductive metalregions with conductivity approximating that of bulk metal.

Metal layers of between 0.3 and 3 microns have been demonstrateddepending on the specific chemistry used. Repeat printing can be used tobuild up thicker layers, such as the 15 to 20 micron layers required foraerial/antenna applications.

EXAMPLE WITH 2 COMPONENT SOLUTIONS

In this example, a component solution, referred to as solution AB,contains both the metal ion and the reducing agent. Solution AB % - byweight copper sulphate 1.63 sodium sulphate 3.21 EDTA disodium salt 0.60formaldehyde solution (37% by weight in water) 0.22 sodium formate 3.71water 85.63 t-butanol 5.00

Solution AB was filtered through a 1 micron GF-B glass fibre filter,available from Whatman.

Deposition was carried out as before, beginning with inkjet printing ofthe catalyst solution followed by a delay while the activator solutionsolvent evaporated. Next, equal volumes of solution AB and solution Cwere inkjet printed over the surface of the substrate using the 64ID3inkjet printhead.

As before, a conductive copper region was formed on the substrate.

EXAMPLE WITH 1 COMPONENT SOLUTION

As a further alternative, the following single solution was prepared. Itis stable for a period of a few hours and so may be inkjet printed as asingle component solution. % - by weight Enplate 872 A 24.09 Enplate 872B 24.09 Enplate 872 C 8.03 water 13.29 ethylene glycol 20 t-butanol 5Surfadone LP-100 0.5 PEG-1500 5

The above solution is prepared from its constituents and then filteredthrough a 1 micron GF-B glass fibre filter from Whatman. The viscosityis 9.8 cPs and the surface tension is 30.0 dynes/cm.

Enplate 872A contains copper sulphate. Enplate 872B contains a cyanidecomplexing agent and formaldehyde. Enplate 872C contains sodiumhydroxide. (Enplate is a trade mark). Enplate 872 A, B and C areavailable from Enthone-OMI and are in common use as component solutionsfor electroless copper plating. Ethylene glycol is present as ahumectant and acts to lower surface tension. T-butanol is a cosolventwhich reduces surface tension and increases wetting. Surfadone LP-100 isa wetting agent with surfactant properties. PEG-1500 functions as ahumectant.

The catalyst solution described above is inkjet printed according to apattern. After a short pause (30 seconds) to allow the solvent in theactivator solution to evaporate, the above solution is deposited byinkjet printing, either across the whole printable area of thesubstrate, or on top of the regions where the activator solution wasinkjet printed. Thus, a copper layer forms on the surface of thesubstrate according to the pattern.

Alternative Activator Solution

The following activator solution can be used as an alternative to theactivator solution given in the examples above. % palladium acetate 2.0diacetone alcohol 47.5 methoxypropanol 47.5 polyvinylbutyral 1.6polyvinylpyrollidinone 1.4

This activator solution has a viscosity of 3.85 cPs and a surfacetension of 30.5 dynes per cm.

K30 grade polyvinylpyrollidinone was sourced from InternationalSpeciality Products. This polymer has a molecule weight between 60,000and 70,000 and was found to accelerate the formation of a conductivemetal region but gave less reproducible results than withpolyvinylbutyral.

1. A method of forming a conductive metal region on a substrate,comprising depositing on the substrate a solution of a metal ion, anddepositing on the substrate a solution of a reducing agent, such thatthe metal ion and the reducing agent react together in a reactionsolution to form a conductive metal region on the substrate.
 2. A methodaccording to claim 1, wherein the conductive metal which is formed onthe substrate constitutes all, or the bulk of, the metal which is toform the conductive metal region in a finished product.
 3. A methodaccording to claim 1 or claim 2, wherein a pH altering reagent is alsodeposited on the substrate, to activate the reducing agent.
 4. A methodaccording to claim 1, wherein the composition of the reaction solutionis selected so that it is sufficiently unstable that the reactionbetween metal ion and the reducing agent in solution to form theconductive metal region on the substrate takes place spontaneously butnot so unstable that a fine powder of conductive metal formsspontaneously throughout the reaction solution, instead of forming aconductive metal region on the substrate.
 5. A method according to claim1, wherein the solution of metal ion and the solution of reducing agentare deposited in a plurality of separate component solutions.
 6. Amethod according to claim 5, wherein the plurality of componentsolutions are deposited sequentially.
 7. A method according to claim 5or claim 6, wherein a single solution, or combination of solutions isallowed to partially or fully dry out, cure or otherwise harden beforeone or more further component solutions are deposited therein.
 8. Amethod according to claim 5, wherein the reaction between the metal ionand the reducing agent in solution to form the conductive metal regionon the substrate is activated by an activator.
 9. A method according toclaim 8, wherein the activator is a second conductive metal differentfrom the first metal.
 10. A method according to claim 9, wherein thesecond metal is formed by depositing ions of the second metal and areducing agent on the substrate, such that the second metal ions and thereducing agent react together in a reaction solution to form aconductive metal region on the surface.
 11. A method according to claim8, wherein the activator has already been applied to the substrate. 12.A method according to claim 8, wherein the activator is a catalyst. 13.A method according to claim 8, wherein the metal ion, the reducing agentand a pH altering reagent are deposited in three separate componentsolutions which mix together on the substrate and form the reactionsolution.
 14. A method according to claim 8, wherein the metal ion andthe reducing agent are deposited in a first component solution, and a pHaltering reagent is deposited in second component solutions, such thatthe first and second component solutions mix together on the substrateand form the reaction solution.
 15. A method according to claim 8,wherein the metal ion, the reducing agent and the pH altering reagentare deposited in a single solution.
 16. A method according to claim 8,wherein the method includes the step of depositing the catalyst on thesubstrate before deposition of a component solution.
 17. A methodaccording to claim 16, wherein the activator is deposited before eitheror both of the metal ion or the reducing agent are deposited on thesubstrate.
 18. A method according to claim 8, wherein the activator isdeposited in an activator solution.
 19. A method according to claim 18,wherein the solvent for the activator solution is primarily or entirelynon-aqueous.
 20. A method according to claim 18 or claim 19, wherein thesolvent is allowed to substantially evaporate or otherwise dissipateprior to deposition of one or more component solutions.
 21. A methodaccording to claim 18, wherein the activator is deposited in a solutionincluding a chemical component which promotes adhesion of the activatorto the substrate.
 22. A method according to claim 8, wherein theactivator is an organic acid salt of a transition metal.
 23. A methodaccording to claim 18, wherein the activator is deposited in a solventselected to partially dissolve the substrate to enable the activator topenetrate the substrate and improve adhesion of the resulting conductivemetal region to the substrate.
 24. A method according to claim 23,wherein the substrate is pretreated prior to the deposition of activatorto improve adhesion.
 25. A method according to claim 18, wherein theactivator solution comprises one or more of the metal ion, the reducingagent or a pH altering reagent.
 26. A method according to claim 5,wherein the component solution which comprises the metal ion furthercomprises a complexing agent.
 27. A method according to claim 8, whereinthe activator is deposited on the substrate in a pattern, therebyleading to the formation of one or more patterned conductive metalregions.
 28. A method according to claim 27, wherein one or morecomponent solutions is deposited in the same pattern, over theactivator.
 29. A method according to claim 5, wherein a pattern isformed by depositing a component solution in a pattern.
 30. A methodaccording to claim 1, wherein deposition in a pattern is carried out byinkjet printing.
 31. A method according to claim 30, wherein anactivator solution and one or more component solutions are inkjetprinted.
 32. A method according to claim 31, wherein substantiallystochiometric amounts of metal ion and reducing agent are deposited. 33.A method according to claim 31, wherein an excess of reducing agent tometal ion is deposited, so that essentially all of the metal ion isconsumed.
 34. A method according to claim 30, in which the reactionsolution or a component solution includes an acid or base, wherein theinkjet print head comprises a ceramic material such that liquidcontaining the acid or base contacts only ceramic material in the inkjetprint head.
 35. A method according to claim 1, wherein the conductivemetal is selected from a group consisting of copper, nickel, silver,gold, cobalt, a platinum group metal, or an alloy of two or more ofthese materials.
 36. A method according to claim 1, wherein theconductive metal includes non-metallic elements.
 37. A method accordingto claim 1, wherein the metal ion is in the form of a salt.
 38. A methodaccording to claim 1, wherein the metal ion is present in a complex. 39.A method according to claim 1, where metal ions of a plurality of metalsare deposited, thereby forming a region of a conductive metal alloy. 40.A method according to claim 1, wherein the substrate and/or the reactionsolution are heated to start and/or speed up the process of depositionof conductive metal on the substrate.
 41. A method according to claim 1,wherein the substrate is a material having thereon electric components.42. A method according to claim 41, including the step of depositing oneor more of said electrical components on a substrate prior to forming aconductive metal region on the resulting substrate.
 43. A methodaccording to claim 1, including the further step of depositing anelectrical component onto the resulting conductive metal region,building up complex devices.
 44. A method according to claim 1, whereinthe method is repeated, depositing further metal ion and reducing agentin solution upon the conductive metal region so as to form a thickerconductive metal layer.
 45. A method according to claim 44, wherein adifferent metal ion is used for a second or successive layers, thusbuilding up a material comprising layers of a plurality of differentmetals.
 46. A method according to claim 1, wherein a solution comprisinga mixture of metal ions is deposited on the substrate, or a plurality ofcomponent solutions comprising different metal ions are deposited on thesubstrate, forming an alloy.
 47. A method according to claim 1, whereina composition of the reaction is initially deposited on the substrateand dried, cured or otherwise hardened to form a solid layer on thesubstrate, with one or more further component liquids subsequentlydeposited on the solid layer.
 48. A method according to claim 47,wherein activator is initially deposited on the substrate and dried,cured or otherwise hardened to form a solid layer.
 49. A methodaccording to claim 48, wherein a solution of a reducing agent and asolution of a metal ion, preferably mixed together, are subsequentlydeposited on the solid layer comprising the activator.
 50. A method offabricating a radio frequency identification tag wherein a conductivemetal region is deposited on a substrate by the method of claim
 1. 51. Amethod according to claim 50, wherein the conductive metal regioncomprises an antenna.
 52. A method of fabricating a radio frequencyidentification tag by depositing a conductive metal region on asubstrate which comprises forming a battery on the substrate by formingdepositing two regions of different conductive metals on the substrateby the method of claim 1, and electrolytically connecting the tworegions by way of an electrolyte, thereby forming an electrochemicalcell.
 53. A method according to claim 52, wherein either or bothconductive metal is deposited by inkjet printing metal ion and reducingagent.
 54. A method according to claim 52, wherein the electrolyte isdeposited by inkjet printing.
 55. A method according to claim 50,wherein the conductive metal region comprises one or more electricalcontacts of the microchip.
 56. An article comprising a substrateincluding a conducting metal region prepared according to the method ofclaim
 1. 57. A method of catalysing the reaction between a metal ion anda reducing agent to form a conducting metal region comprising the use ofan organic acid salt of a transition metal as a catalyst.
 58. A methodaccording to claim 57, wherein the transition metal is palladium.
 59. Amethod according to claim 58, wherein the organic acid salt is acetate,propanoate or butanoate.
 60. A method according to claim 57, wherein thecatalyst is deposited with a polymer to adhere the catalyst to thesubstrate.
 61. A method according to claim 57, wherein the catalyst isapplied to a substrate and the conducting metal region is formed as alayer on the substrate.
 62. A method according to claim 57, wherein thecatalyst is added to the substrate by inkjet printing a solutionincluding the catalyst.